1. Field of the Invention
The invention relates in general to an operating method and a display panel using the same, and more particularly to an operating method for a multi-bit memory in pixel (MIP) and a display panel using the same.
2. Description of the Related Art
Display devices have been widespread used in a variety of applications, such as lap-top computers, mobile phones, or personal digital assistants. As to a display device, the number of bit, or bit depth is associated with the visual quality of displayed images. As is defined in computer graphics, color depth or bit depth is the number of bits used to represent the color or gray levels of a single pixel in a bitmapped image or video frame buffer. This concept is also known as bits per pixel (BPP), particularly when specified along with the number of bits used. Higher number of bits usually gives a broader range of distinct colors or gray levels.
As an additional feature of display devices, a memory in pixel (MIP), which is considered for reducing power consumption, has a pixel memory which can be used to maintain the gray level of the MIP without new data being provided from a source driver, so that power consumption can be reduced. In general, applying intermediate voltages to a pixel generates a number of gray levels in display. A multi-bit MIP, when being requested to generate a constant gray level, is refreshed by detecting its pixel voltage, which determines which gray level the pixel has, or more generally identifies what kind of image data the pixel is previously stored. At this time, the threshold voltage of switches used in the multi-bit MIP is served as a basic voltage interval at which these intermediate voltages are spaced. If the stored image data can be correctly identified, the multi-bit MIP can be correctly refreshed thereafter.
However, there is a problem with refresh operation of the multi-bit MIP. In the multi-bit MIP, the number of bits is increased by reducing the voltage difference corresponding to two adjacent grey levels, so that more intermediate voltages can be assigned to describe more grey levels, thereby providing an increased number of bits. Due to the manufactured process of the display devices, the threshold voltage variation is diverse with respect to difference display devices. As such, when the voltage difference corresponding to two adjacent grey levels becomes too small, there is a problem with refresh operation that it is critical, sometimes impossible to identify what kind of image data the pixel is stored with. Therefore, the reliability of refresh operation is reduced, resulting in a limited number of bits per pixel.